(a) Field of the Invention
The present invention relates to a method for traffic indication and channel adaptation for terminals in a sleep mode, and an apparatus therefore. More specifically, the present invention relates to a method and apparatus for allowing a terminal in a sleep mode to enter an awake mode by a traffic indication and adaptively transmitting data according to channel quality information (CQI) of the terminal in a mobile communication or a wireless portable internet system.
(b) Description of the Related Art
The wireless portable internet system is a next generation communication system providing further mobility to short-distance data communication using a stationary access point in a like manner of a wireless local area network (LAN).
Various international standards for the wireless portable internet system have been suggested by the IEEE 802.16e working group.
As to a conventional traffic indication and channel adaptation method, when traffic occurs at a subscriber station in the sleep mode, the subscriber station enters to the awake mode according to a traffic indication message, and downlink data are transmitted to the subscriber station, and hence, it is difficult to apply an appropriate adaptive modulation and coding level to the subscriber station.
With reference to FIGS. 1 and 2, a conventional traffic indication and channel adaptation process for the subscriber station in the sleep mode will be described. FIG. 1 shows a diagram representing the conventional traffic indication and channel adaptation process for the subscriber station in the sleep mode. At this time, a transverse axis represents a time progress, BS denotes a base station, and SS denotes a subscriber station.
As shown in FIG. 1, a subscriber station SS receives a traffic indication (TRF-IND) message from a base station BS in step S101, and acknowledges the presence of downlink traffic for the subscriber station SS. The subscriber station SS requests a bandwidth by transmitting a bandwidth request (BW-REQ) message to the base station in order to report channel quality information (CQI) in step S102 when a radio channel of the subscriber station SS is different from the same in the sleep mode.
The subscriber station receives an uplink resource allocation (UL-MAP) message from the base station BS, and an uplink resource for transmitting a CQI result is allocated in step S103.
The subscriber station SS reports the channel quality estimation result to the base station BS by using the uplink resource in step S104. In detail, the subscriber station SS reports the channel quality estimation result by transmitting a ranging request (RNG-REQ) message having a report-response (REP-RSP) message, a downlink burst profile change request (DBPC-REQ) message, or a preferred burst profile (Preferred-DIUC) value as parameters to the base station BS.
The base station BS transmits downlink data (user data) in step S105 by applying the appropriate adaptive modulation and coding level for the subscriber station SS with reference to the channel quality estimation result.
However, a delay caused by the uplink bandwidth request and allocation in steps S101 and S102 is inevitably provided until the channel quality estimation result is reported to the base station BS in step S104 because the uplink resource allocation for reporting the channel quality estimation result is not premised. Accordingly, it is difficult to deal with quick changes of channel environments, and to satisfy the quality of service (QoS).
FIG. 2 shows a diagram representing a traffic indication and channel adaptation process for the subscriber station in the sleep mode when a contention based bandwidth is requested.
As shown in FIG. 2, the subscriber station SS receives the traffic indication (TRF-IND) message from the base station BS in step S201, acknowledges the presence of downlink traffic for the subscriber station SS, and transmits a contention-based bandwidth request (Contention-based BW-REQ) message to the base station BS in step S202. At this time, a timer for waiting for a response message expires when the bandwidth request is failed due to a conflict of the requests.
As described above, when the contention-based random access is failed, the subscriber station SS performs a backoff process in step S203 and reperforms the contention-based bandwidth request in step S204.
When the bandwidth request is successfully performed, the base station BS transmits the UL-MAP message to the subscriber station SS to allocate the uplink resource in step S205.
The subscriber station SS reports the channel quality estimation result by the uplink resource in step S206. At this time, the subscriber station SS reports a burst profile for downlink transmission which is the channel quality estimation result to the base station when the base station BS determines the modulation and coding level.
When determining the modulation and coding level, the subscriber is station SS uses the DBPC-REQ message to request the bandwidth for the purpose of using a predetermined profile. At this time, an unwanted delay may occur because the bandwidth request is performed in the contention based access, and therefore the radio resources may be wasted, and the appropriate adaptive modulation and coding level is difficult to determine.
In the conventional traffic indication method, the downlink data is transmitted to the subscriber station once the subscriber station is awakened by the traffic indication. Accordingly, it may be impossible for the subscriber station to receive the data because an actual channel environment is different from a channel environment acknowledged by the base station when the base station transmits the data by applying the modulation and coding level before the sleep mode.
The downlink data is transmitted by using the most effective modulation and coding method in order to prevent the above problem. However, it may cause the radio resources to be wasted. In addition, the downlink data transmitted by the base station is wasted when the subscriber station does not properly receive the traffic indication message because there is no acknowledgement for the traffic indication.
Furthermore, to determine the adaptive modulation and coding level in the prior art, the subscriber station requests the uplink bandwidth a random access and uses the allocated uplink resource to report the radio channel quality information when the subscriber station in the sleep mode receives the traffic indication.
However, it is still difficult to determine the appropriate adaptive modulation and coding level because the delay caused by the random access is inevitably generated, and the radio resources are also wasted by the unnecessary random access.